Mold



Patented Nov. 21, 1944 MOLD Edward H. Wallace, Detroit, Mich., assignorto United States N. Y.,

Rubber Company, a corporation of New Jersey New York,

Application January 10, 1942, Serial No. 426,337

` (ci. 11s- 41) Claims.

This invention relates to molds. More particuface layer and a layer ofnon-resilient material attached to the resilient layer'for the purposeof supporting and maintaining the first named layer in a relatively4fixed position.

In the manufacture of molds for reproduction purposes and in which theoriginal or master from which the mold is to be made containsindentations or other irregularities, it has been customary to apply alayer of rubber to the master. The rubber is usually applied in the formof la latex composition, and the article or master is dipped into thelatex to provide thereon a series of sucessive coats, or the latex maybe sprayed directly on the master. In either case, the rubber followsall the detailed formations on the master and provides a surface whichis an accurate reverse replica of the master. One of the principalobjections to this practice is that, after removal of the master, it isdifllcult to maintain the accurate dimensions originally imparted to therubber layer due to the resiliency of the rubber. I have found that by aspecial treatment wherebyl the exposed surface of the rubber layer couldbe formed with many irregularities that a solid substance, such asplaster of Paris, could be readily attached to the rubber layer. Uponhardening of the plaster of Paris, the rubber layer becomes firmlyattached thereto; thus, the original dimensions of the rubber layer areaccurately preserved.

It is, therefore, among the objects of my invention to provide a rigidbacking interlocked with flexible molding surface; to provide areinf-orced flexible lmold surface capable of retaining the accuratedimensions of the master; and to provide a mold which may be preparedeconomicallyand expeditiously. These and other objects and advantageswill appear more fully in the following detailed description whenconsidered with the accompanying drawing in which:

Fig. 1 is a side elevational view of an original article or master, suchas, a baseball which is l illustrative as van article for reproduction;

Fig. 2 is a side elevational view of the master imbedded in means topermit a one-half reproduction;

Fig. 3 is a transversed view, in section, of the master supportingmeans, rubber surface layer and backing;

Fig. 4 is a perspective view illustrating the :finished mold andcomprising the rubber surface layer and backing; ,5

Fig. 5 is a transversed view 'in section of the I larly it relates to amold having a resilient suris employed, and a layer ofv latex in theorderl Dir rubber surface layer and a replica of the original article;

Fig. 6 is aside elevational replica;

Fig. 7 is an enlarged `detailed view, in section, of a portion of therubber surface layer illustrating a surface formation; and,

Fig. 8 is a transversed view, in section, illustrating a modification ofthe application shown in Fig. 3.

With reference to the drawing, and in particular to Fig. 1, I show anoriginal article, or master I, in the form of a baseball. However, it isto be understood that the baseball is illustrated for exemplary purposesonly and that various other articles or shapes may be substitutedtherefor. A baseball has been illustrated because of the fine detailrequired to obtain a reproduction thereof, particularlywith reference tothe stitching and the minute details accompanying the stitching and thespace thus formed by the marginal edges of the baseball cover. In orderto obtain a replica from the master l, it is general practice in casesof this kind where the master is spherical in form to provide adiametrical parting line to reduce the master for a. one-halfreproduction. This is accomplished by any cor.- ventional means, suchas, by embedding the master l in a plaster of Paris support 2, as shownin Fig. 2. The master l is suspended in the plaster of Paris while theplaster is in a fluid state, and the parting surface is formed as the'plaster har-dens, thus one-half of the master l projects from thesupport 2.

Directily upon the exposed surface of the masview of the complete terand the adjoining surface of the support 2 is formed a layer 3 ofresilient material, such as a rubber composition. Preferably, this:layer is formed by spraying latex, or the equivalent artificialdispersion of rubber or rubber-like material, directly againstthe moldsurface. In order to accomplish this, a conventional spray gun of 1,64,inch thick is applied to the mold surface.

ectily after the application of the latex, a coagulant, such as, amixture of alcohol and acetic acid is applied. The coagulant is alsoapplied by a spray gun or other convenient means for effecting a depositover the latex. After the treatment with the coagulant, the layer isallowed to dry for a short period of about five minutes, and'additionalcoatings are applied in the same manner. This is continued until adesired thickness is obtained. When the rubber layer is formed over amaster in which there is little or no undercut- 4ing projections 4(Figi).

' thoroughly dried,

ting, the total thickness of the layer 3 may be on the order of le inch.However, where the master includes undercuts and irregularities, thethickness of the vlayer 3 is increased to a point where the elasticityof the rubber will permit easy separation of the layer from the master.The following is an example of a. latex composition which may be usedtoform the layer t:

` Prevulcanized later Rubber (60% total solids) parts 100 Stabilizer dov 0.5 Sulfur do- 0.25 Activator do 0.5 Accelerator do 0.5 VAntioxidantdo. 0.5 Carbon black do 1.0

" Total solids percent-- 57.0

I After the layer 3 has been built up to the desired thickness by theapplication of successive 'coats of latex, the outer surface of thelayer is relative to the layer 3 may be rotated over an angle up to180"l with the result that nodules E are formed on the outermost tips ofthe projections t. These nodules or enlarged portions serve to functionas a locking means with material subsequently applied against the outersurface of layer 3. After the layer 3, together with its projections dand n ules E are formed, the layer is dried for a period of about tenhours at room tem-V perature or about two hours atl 140 F.

, A backing material is next applied to the surface o f the layer t.Preferably, this supporting material is in the form of a backing 6 ofplaster of Paris cast directly against the surface rof the layer .3 andallowed to harden thereagainst. After the plaster has set, theapplication of heat is desirable. As a result of the application of theplaster 'E to the layer 3, the projections and nodules formed on theexterior surface of layer 3 become embedded in the plaster 6 and are Atherefore rigidly adhered to the plaster.

Figure 8 illustrates a modification of the-disclosure shown in Figure 3and shows a backing materiall -in the form of a metal of low meltingpoint, -such as,lead or solder, formed -directly against the'surface ofthe layer 3. The metal or byspraying the metal against the surface. *Ineither case a rigid backing is formed which bethus establishing itsdimensions accurately. l

After the plaster backing 8 andthe layer 3 are the backing 6 togetherwith the from the master I.

layer is stripped adherence between the backing and layer prevents anyVperrianentdis rtion of the layer 3 during the stripping operationandmaintains the layer 3 in a position for convenient handling duringsubsethe projections. have been formed, the position of the spray gunthe mold cavity, formed by silient, such as,

, surface of the resilient e may be applied directly to the layer 3 bycasting comes interlocked with the layer 3 to maintain f the resilientlayer in a ilxed position,

The rigid,l

face details as present in the rubber Vlayer 3. This can be accomplishedby casting or spraying into the layer 3, a deposit 8 of an alloy havinga low melting point. .In such case the alloy, for example,\Cerrobase,which is a lead bismuth alloy having a. melting point of about 254 F.,e. with the result that a half replica is formedl of the original masterI, such as shown in Figure '6. This replica contains all the detail andundercut portions that are characteristic of the original master l. Itis to be understood that the mold, formed by the layer 3 and backing 6may be employed as a nished mold within which finished products may bemolded, providing that the product can be formed against the rubber1;ayer without substantially deteriorating the rubber. l An example ofpreferable materials are plaster, plastics, or other substances that maybe nriolded in a liquid state and subsequently solidified. This replica8 may now be used man electroforming Abath anda layer of ironelectrodepositing thereon after which the replica 3 is melted therefromleaving a completed iron mold having all the del tail. characteristicsl-liay"z ing thus obtained repeatedly in the formation of e.` replica ofthe original master of a composition which is rerubber. While alone-haii moldL is illustrated, it is to be understood that the otherhalf of the mold may .be formed in substantially the same manner toproduce a` completed article of the original master.

such as the spherical baseball illustrated 'in Figure l..

to be understood that the invention is susceptible or thosemodifications which appear obviously within the spirit of the inventionand as dened within the scope of the appended claims.

Having thus described my invention, desire to protect by Letters Patentis:

l. A mold comprising, a layer of resilient material one surface of whichforms the mold face, a multiplicity o irregularly shaped projections ofresilient material extending from the opposite layer and a backing ofrigid material contacting the said opposite sur face of the resilientlayer, said irregularly shaped projections being embedded in the rigidmaterial and locking the backing to the resilient layer.

2. A mold comprising, -a layer of resilient ma-` terial one surface of.which forms the mold face, Va multiplicity of irregularly shapedprojections of resilient material integral withand extending Afrom theopposite surface of the resilient layer and at least some of saidprojections having enlarged nodules at the tips thereof, and a backingof rigid material contacting the said opposite surface of the resilientlayer, said nodules being embedded in the rigid material and locking thebacking to the resilient layer.

3. A mold comprising, a layer of rubber one surface of which forms themold face, a multiwhat l plicity of irregularly shaped rubberprojections extending from the opposite surface of the rubber is cast inthe cavity of the layer y an iron mold, it may be used projections andprojections embedded in the plaster of Paris and locking the backing tothe rubber layer. j

4. IA mold comprising, a layer of rubber one surface of which forms themold face, a multiplicity of irregularly shaped rubber projectionsintegral with and extending from the opposite surface of the rubberlayer and at least some of the said projections having enlarged nodulesat the tips thereof, and a backing of plaster of Paris contacting thesaid opposite surface of the rubber layerpsaid rubber lprojections andnodules being embedded in the plaster of Paris and locking the backingto the rubber layer.

5. A mold comprising, a layer of rubber one surface of which forms themold face, a multi- 5 plicity of irregularly shaped rubber p.ojections10 and locking the backing to the rubber layer.

' EDWARD H. WALLACE.

